Peach tree chilling requirements

CHILLING REQUIREMENTS OF SELECTED PEACH VARIETIES

M.L. Parker, Extension Specialist D.J. Werner, Professor

Peach trees are deciduous and drop their leaves in the Fall and go into a developmental state known as dormancy. As the winter progresses the trees go into another state known as rest, during which they cannot grow even if environmental conditions are favorable for tree growth. Exposure to chilling temperatures is necessary to overcome this period of rest, after which normal bud break and growth can begin once growing conditions are favorable. The minimal necessary duration of chilling length for any particular variety is known as the chilling requirement for that variety. Temperatures effective in satisfying the chilling requirement normally range from 32 F to 50 F, with the optimal temperature being approximately 45 F. North Carolina typically receives in excess of 1,000 chilling hours annually.

Peach varieties vary greatly in the number of chilling hours required from less than 200 hours to over 1,000 hours. The lower the chilling requirement, the earlier the tree will begin growing once temperatures are warm enough. The dilemma that is faced in North Carolina is the large fluctuation in winter and spring temperatures. For low chilling requirement varieties, the chilling requirement is quickly met during winter. Once the chilling requirement is met any warm period during the remainder of the winter will cause peach trees to prematurely bloom, and the blossoms will be killed by the next freezing temperature. However, for high chilling requirement varieties, if the chilling requirement is not met, trees will bloom very erratically, produce deformed leaves and have little to no fruit set in the spring. The latter scenario of insufficient chilling rarely occurs in North Carolina.

In North Carolina, only varieties with a chilling requirement of 750 hours or greater are recommended to minimize frost/freeze crop losses. Varieties with a chilling requirement less than 750 hours are grown in North Carolina; however they are grown with a high probability of frequent crop loss and are not recommended for large plantings.

Table 1 lists many commercial peach varieties and their chilling requirement. Varietal inclusion in Table 1 is not an endorsement of such variety.